The best email subject lines are enticing, coercing the readers to click on the single link you provided in the body of your email... usually with a mispelled word or a grammatical error... because that way it has real class, it communicates that you (the sender) are not trying to exploit them, but that you're a human being with flaws and vulnerabilities, and gives your email the exotic look that perhaps you're not a master of the language you wrote the email in... If you do provide a message in your email, it should be filled with promises about increasing libido, or the promise that if one clicks on that link they're going to laugh some part of their anatomy completely off their body.